JPH10228630A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium having improved electromagnetic conversion characteristics, in particular high density recording characteristics and excellent durability and showing an improved error rate in particular in a high density recording region. SOLUTION: This magnetic recording medium is produced by forming a base layer which is substantially nonmagnetic and a magnetic layer having dispersion of a ferromagnetic metal fine powder or a ferromagnetic hexagonal ferrite fine powder in a binder in this order on a supporting body. In this magnetic recording medium, signals of 0.2 to 2Gbit/inch<2> area recording density can be recorded. The magnetic layer has 0.05 to 0.25μm dry film thickness, 8.0×10<-3> to 1.0×10<-3> emu/cm<2> Φm, and >=1800Oe coercive force. The base layer and/or the magnetic layer contains at least a satd. fatty acid, an unsatd. fatty acid and a satd. or unsatd. fatty acid ester.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a coating type magnetic recording medium having a high recording density. In particular, the present invention relates to a magnetic recording medium for high-density recording, which has a magnetic layer and a substantially nonmagnetic lower layer, and includes a ferromagnetic metal fine powder or a hexagonal ferrite fine powder in the uppermost layer.

[0002]

2. Description of the Related Art In the field of magnetic disks, 2 MB MF-2HD floppy disks using Co-modified iron oxide have been standardly mounted on personal computers. However, in today's rapidly increasing data capacity, the capacity cannot be said to be sufficient, and it has been desired to increase the capacity of floppy disks.

In the field of magnetic tapes, in recent years, with the spread of office computers such as minicomputers, personal computers, and workstations, magnetic tapes for recording computer data as external storage media (so-called backup tapes).
Research is being actively conducted. In practical use of magnetic tapes for such applications, especially with the downsizing of computers and the increase in information processing capacity, the increase in recording capacity,
In order to achieve miniaturization, improvement in recording capacity is strongly required.

Conventionally, a magnetic recording medium has a magnetic layer obtained by dispersing iron oxide, Co-modified iron oxide, CrO ₂ , ferromagnetic metal powder, and hexagonal ferrite powder in a binder on a non-magnetic support. Is widely used. Among them, ferromagnetic metal fine powder and hexagonal ferrite fine powder are known to have excellent high density recording characteristics. In the case of a disk, a 10-MB MF-2TD and a 21-MB MF are used as large-capacity disks using ferromagnetic metal fine powder having excellent high-density recording characteristics.
Large-capacity disks using 2SD or hexagonal ferrite include 4MB MF-2ED, 21MB floptical, and the like, but were not sufficient in capacity and performance. Under such circumstances, many attempts have been made to improve the high-density recording characteristics. An example is shown below.

In order to improve the characteristics of a disk-shaped magnetic recording medium, Japanese Patent Application Laid-Open No. 64-84418 proposes to use a vinyl chloride resin having an acidic group, an epoxy group and a hydroxyl group. It is proposed to use a metal fine powder having a Hc of 1000 Oe or more and a specific surface area of 25 to 70 m ² / g. I have.

In order to improve the durability of a disk-shaped magnetic recording medium, Japanese Patent Publication No. 7-85304 proposes to use a fatty acid ester having an unsaturated bond with an unsaturated fatty acid ester. It has been proposed to use a fatty acid ester having a fatty acid ester and an ether bond, and JP-A-54-124716 proposes to include a non-magnetic powder having a Mohs hardness of 6 or more and a higher fatty acid ester. Has a volume and surface roughness of 0.005 to 0.025
μm is proposed in Japanese Patent Application Laid-Open No. 61-294637.
It is proposed to use a low melting point and a high melting point fatty acid ester in JP-B-7-36216.
It has been proposed to use an abrasive having a particle size of ４ to ／ and a fatty acid ester having a low melting point.

As a configuration of a disk-shaped magnetic recording medium having a nonmagnetic lower layer and an intermediate layer, a configuration having a conductive layer and a magnetic layer containing metal fine powder is proposed in JP-A-3-120613. Has proposed a structure having a magnetic layer and a non-magnetic layer of 1 μm or less.
9337 proposes a configuration including a carbon intermediate layer and a magnetic layer containing a lubricant, and JP-A-5-290358 proposes a configuration having a nonmagnetic layer having a defined carbon size.

On the other hand, a disk-shaped magnetic recording medium comprising a thin magnetic layer and a functional non-magnetic layer has recently been developed.
0MB class floppy disks have appeared. Japanese Patent Application Laid-Open No. 5-109061 shows these features.
Has proposed a configuration having a magnetic layer having a Hc of 1400 Oe or more and a thickness of 0.5 μm or less and a non-magnetic layer containing conductive particles, and Japanese Patent Application Laid-Open No. 5-197946 discloses a configuration containing an abrasive larger than the magnetic layer thickness. Japanese Patent Application Laid-Open No. Hei 6-68453 proposes a configuration in which the thickness of a magnetic layer is 0.5 μm or less, the thickness variation of the magnetic layer is within ± 15%, and the surface electric resistance is specified. A configuration has been proposed in which two types of abrasives having different diameters are included and the amount of the abrasive on the surface is regulated.

In recent years, with the spread of office computers such as minicomputers and personal computers, researches on magnetic tapes (so-called backup tapes) for recording computer data as external storage media have been made with respect to tape-shaped magnetic recording media. Is being actively conducted. When a magnetic tape for such a purpose is put to practical use, especially in connection with the miniaturization of computers and the increase in information processing capacity, an increase in recording capacity is strongly demanded in order to achieve large-capacity recording and miniaturization. In addition, the use environment of magnetic tapes is widespread, so it can be used under a wide range of environmental conditions (especially in the circumstance where temperature and humidity fluctuates rapidly). Reliability for performance such as recording and reading is required more than before.

Conventionally, a magnetic tape used in a digital signal recording system is determined for each system, and a so-called DLT type, 3480, 3490, 3590,
Magnetic tapes compatible with QIC, D8 type, or DDS type are known. In any system, the magnetic tape used is composed of a relatively thick single-layer ferromagnetic powder having a thickness of 2.0 to 3.0 μm, a binder, and a polishing agent on one side of the nonmagnetic support. A magnetic layer containing an agent is provided, and a back coat layer is provided on the other side to prevent winding disturbance and maintain good running durability.
However, in the magnetic layer having a relatively thick single-layer structure as described above, there is a problem of a loss in thickness that the output is reduced.

It is known that the magnetic layer is made thinner in order to improve the reduction of the reproduction output due to the thickness loss of the magnetic layer. For example, Japanese Patent Application Laid-Open No. 5-182178 discloses that A lower nonmagnetic layer containing an inorganic powder and dispersed in a binder, and an upper magnetic layer having a thickness of 1.0 μm or less formed by dispersing a ferromagnetic powder in the binder while the nonmagnetic layer is in a wet state. Disclosed a magnetic recording medium.

However, with the rapid increase in capacity and density of magnetic recording media in the form of disks or tapes, it has become difficult to obtain satisfactory characteristics even with such techniques. Also, it is becoming difficult to achieve both durability and durability.

[0013]

SUMMARY OF THE INVENTION According to the present invention, there is provided a magnetic recording medium in which electromagnetic characteristics, particularly high-density recording characteristics, are remarkably improved and excellent durability is provided, and an error rate in a high-density recording region is remarkably improved. It is intended to provide a recording medium. In particular, it is an object of the present invention to provide a large-capacity disk-shaped magnetic recording medium having a recording capacity of 0.2 to 2 Gbit, particularly preferably 0.35 to 2 Gbit.

[0014]

Means for Solving the Problems The present inventors have conducted intensive studies to obtain a magnetic recording medium having good electromagnetic conversion characteristics and durability and a particularly improved error rate in a high-density recording area. It has been found that by using the following medium, excellent high-density recording characteristics and excellent durability, which are the objects of the present invention, can be obtained, and the present invention has been accomplished.

That is, in the present invention, a substantially non-magnetic lower layer and a magnetic layer formed by dispersing a ferromagnetic metal fine powder or a ferromagnetic hexagonal ferrite fine powder in a binder are provided in this order on a support. In the magnetic recording medium, the areal recording density of the magnetic recording medium is 0.2 to ² Gbit / inch ² , the dry thickness of the magnetic layer is 0.05 to 0.25 μm, and φm is 8.0 × 10 ^{-3 to} 1.0 × 10 ⁻³ emu / cm ² , the coercive force of the magnetic layer is 1800 Oe or more, and the lower layer and / or the magnetic layer is at least a saturated fatty acid,
By using a magnetic recording medium characterized by containing unsaturated fatty acids and saturated or unsaturated fatty acid esters, it has both high density characteristics and excellent durability that could not be obtained by conventional techniques, and It has been found that a magnetic recording medium having a significantly improved error rate in a recording area can be obtained.

Here, the substantially non-magnetic lower layer means that it may have a magnetic property to the extent that it does not participate in recording, and is hereinafter simply referred to as the lower layer or the non-magnetic layer. The surface recording density is obtained by multiplying the linear recording density by the track density. φm is the amount of magnetic moment (emu / cm ² ) that can be measured directly from the magnetic layer per unit area on one side using a vibrating sample magnetometer (VSM: manufactured by Toei Kogyo Co., Ltd.) at Hm 10 kOe. The required magnetic flux density Bm (unit G = 4πemu / cm ³ ) and thickness (cm)
Multiplied by. Therefore, the unit of φm is emu / c
It is expressed in m ² or G · cm.

The linear recording density is the number of bits of a signal to be recorded per inch in the recording direction. These linear recording density, track density, and areal recording density are values determined by the system. That is, in the present invention, in order to improve the areal recording density, the magnetic layer thickness, the magnetic layer Hc, and the center plane average surface roughness were improved in terms of the linear recording density, and Φm was optimized in terms of the track density. Things.

Preferred embodiments of the present invention are as follows. (1) The magnetic recording medium has a surface recording density of 0.35.
A magnetic recording medium for recording signals of up to ² Gbit / inch ² , wherein the lower layer contains an inorganic powder having a Mohs hardness of 4 or more. (2) The dry thickness of the magnetic layer is 0.05 to 0.20 μm
m, and the average particle size in the magnetic layer is 0.4
A magnetic recording medium comprising an abrasive having a size of not more than μm. (3) A magnetic recording medium, wherein the coercive force of the magnetic layer is 2000 Oe or more. (4) The saturated fatty acids and unsaturated fatty acids have 10 to 10 carbon atoms.
24. A magnetic recording medium comprising 24 monobasic fatty acids (which may be branched). (5) The saturated or unsaturated fatty acid ester has 10 carbon atoms.
~ 24 monobasic fatty acids (may be branched)
And mono-, di-, tri-, tetra-, penta-, and hexa-valent alcohols having 2 to 12 carbon atoms (which may be branched). A magnetic recording medium, which is a fatty acid ester of a monoalkyl ether of an ester, a trifatty acid ester, or an alkylene oxide polymer. (6) The magnetic recording medium, wherein the magnetic recording medium is a disk. (7) The magnetic recording medium, wherein the magnetic recording medium is a computer tape.

[0019] With the magnetic the surface recording density can not be obtained with prior art 0.2~2Gbit / inch ² further areal density recording signals of 0.35~2Gbit / inch ² It has been found that it is possible to obtain a magnetic recording medium having excellent high-density characteristics and excellent durability and having a particularly improved error rate particularly in a high-density region, particularly a disk-shaped magnetic recording medium. It is a thing. According to the present invention, the excellent areal recording density is 0.2 to 2 Gbi.
t / inch ² Further, the areal recording density is 0.35 to ² Gbit / inch ²
In other words, the following magnetic recording media with high density characteristics and excellent durability, especially disk-shaped magnetic recording media, which have never been achieved with products known to the world in coating type magnetic recording media, were obtained. It is the result of combining these points organically and integrating them.

The points of the present invention are high Hc, super smoothness,
Improved durability by improving composite lubricants, highly durable binders and ferromagnetic powders, ultra-thin magnetic layers and reduced fluctuations at the interface with the lower layer, high filling of powders (ferromagnetic powders and non-magnetic powders) ,
Ultra fine particles of powder (ferromagnetic powder, non-magnetic powder), stabilization of head touch, dimensional stability and servo, improvement of thermal shrinkage of magnetic layer and support, action of lubricant at high and low temperature, etc. These were combined, and as a result of the synthesis, the present invention was achieved.

[0021] In the field of personal computers, which are becoming increasingly multi-media, attention has been paid to large-capacity recording media replacing conventional floppy disks, and they have been sold as ZIP disks by IOMEGA (Iomega), Inc. of the United States. This is an ATOMM (Advanced S) developed by the present applicant.
upper Thin Layer & High Ou
input Metal Media Technology
gy), a recording medium having a lower layer and a thin magnetic layer, and a product having a recording capacity of 3.7 inches and a recording capacity of 100 MB or more is sold. 100-120MB capacity is MO
(3.5 inches), and one newspaper article can fit in July or August. The transfer rate indicating the write / read time of data (information) is 2 MB or more per second, which is comparable to that of a hard disk.
20 times faster than MO and more than twice as fast as MO. Further, this recording medium having a lower layer and a thin magnetic layer can be mass-produced with the same coating type medium as that of the current FD, and has an advantage that it is lower in price than an MO or a hard disk.

The present inventors have conducted intensive studies based on the knowledge of such media, and as a result, have found that the ZIP disk and MO
(3.5 inches), the areal recording density which is much larger than the recording capacity is 0.2 to ² Gbit / inch ^{2 and} the areal recording density is 0.3
A magnetic recording medium having both high density characteristics and excellent durability, which has never been achieved in a product known to the world as 5 to ² Gbit / inch ² , and in particular, an error rate in a high density recording area is remarkably improved, In particular, a disk-shaped magnetic recording medium is obtained, which is an invention applicable to a magnetic tape such as a computer tape.

The magnetic recording medium of the present invention contains an ultra-thin magnetic layer containing ultra-fine magnetic powder having high output and high dispersibility, and a lower layer containing a spherical or acicular inorganic powder. By reducing the thickness, the canceling of the magnetic force in the magnetic layer is reduced, the output in the high frequency region is greatly increased, and the overwriting characteristics are also improved. By improving the magnetic head, the effect of the ultra-thin magnetic layer can be further exhibited in combination with the narrow gap head, and the digital recording characteristics can be improved.

The thickness of the upper magnetic layer is selected to be as thin as 0.05 to 0.25 μm so as to match the magnetic recording method for high-density recording and the performance required from the magnetic head. Such ultra-thin magnetic layer, which is uniform and thin, has a high degree of packing by highly dispersing fine magnetic powder and non-magnetic powder by using a dispersant and a combination of highly dispersible binders. . The magnetic material used is a magnetic material excellent in high output, high dispersion and high randomization in order to maximize the suitability of a large capacity FD or computer tape. That is, by using a ferromagnetic metal fine powder or a ferromagnetic hexagonal ferrite fine powder which can achieve high output with very fine particles,
In particular, the major axis length is 0.1 μm or less, and
When it is Ａ180 A, high output and high durability can be achieved by further containing Co, and by containing Al or Y as a sintering inhibitor. In order to achieve a high transfer rate, a three-dimensional network binder system suitable for an ultra-thin magnetic layer is used to ensure running stability and durability during high-speed rotation. In addition, a composite lubricant that can maintain its effectiveness even when used under a wide range of temperature and humidity conditions or when used at high speeds is arranged in the upper and lower layers. An appropriate amount of lubricant is always supplied to the layer, the durability of the upper magnetic layer is increased, and the reliability is improved. Further, the cushion effect of the lower layer can provide good head touch and stable running performance.

In a large-capacity recording system, a high transfer rate is required. For this purpose, it is necessary to increase the number of rotations of the magnetic disk by one digit or more compared to the conventional FD system. As the capacity and density of magnetic recording increase, the recording track density increases. In general, a servo recording area is provided on a medium to ensure traceability of a magnetic head with respect to a recording track. In the magnetic recording medium of the present invention, a base having enhanced isotropic dimensional stability is used as a support base to further stabilize traceability. By using an ultra-smooth base, the smoothness of the magnetic layer can be further improved.

In order to increase the density of disk-shaped magnetic recording,
It is necessary to improve the linear recording density and the track density. Of these, the characteristics of the support are important for improving the track density. In the medium of the present invention, the dimensional stability of the support base, particularly the isotropy, is considered. Servo recording is an indispensable technique in recording / reproducing at a high track density, but this improvement can be achieved from the medium side by making the support base as isotropic as possible.

The advantages of the present invention in which the magnetic layer is changed from a single layer to an ATOMM structure are considered as follows. (1) Improvement of electromagnetic conversion characteristics by thinning the magnetic layer, (2) Improvement of durability by stable supply of lubricant (3) High output by smoothing the upper magnetic layer (4) Separation of functions of the magnetic layer These functions cannot be achieved simply by layering the magnetic layers. In order to configure a multilayer structure, a “sequential multilayer system” in which layers are sequentially configured is generally used. In this method, first, a lower layer is applied, cured or dried, and then an upper magnetic layer is similarly applied, cured, and surface-treated. The FD differs from the magnetic tape in that the same processing is performed on both sides. After the coating process, it is completed as a final product through a slitting process, a punching process, a shell assembling process, and a certifying process.

By forming a thin magnetic layer, the following electromagnetic conversion characteristics can be greatly improved. (1) Improvement of the output in the high frequency region by improving the characteristics at the time of recording demagnetization, (2) Improvement of the overwriting (overwrite) characteristics (3) Ensuring the window margin Durability is an important factor for the magnetic disk. Particularly, in order to realize a high transfer rate, it is necessary to increase the number of rotations of the magnetic disk by one digit or more compared with the conventional FD system, and the medium durability when the medium in the magnetic head / cartridge slides at high speed with the medium. Is an important issue.
As means for improving the durability of the medium, there are a binder formulation for increasing the film strength of the disk itself and a lubricant formulation for maintaining the slipperiness with the magnetic head. In the medium of the present invention, a three-dimensional network binder system which has been proven in the current FD system is improved in the binder formulation.

The lubricant is used in combination with a plurality of lubricants that exhibit excellent effects under various temperature and humidity environments used, and has a wide range of temperature (low temperature, room temperature, high temperature) and humidity (low humidity, high humidity). Even under a wet environment, each lubricant exerts its function and can maintain a totally stable lubricating effect. In addition, by utilizing the structure of the upper and lower two layers, the lower layer has a lubricant tank effect so that an appropriate amount of lubricant is always supplied to the upper magnetic layer, and the durability of the upper magnetic layer can be improved. Things. There is a limit to the amount of lubricant that can be included in the ultra-thin magnetic layer, and simply thinning the magnetic layer reduces the absolute amount of lubricant, leading to deterioration in running durability. In this case, it was difficult to obtain a balance between the two. The upper and lower layers are provided with different functions and complement each other to achieve both improved electromagnetic conversion characteristics and improved durability. This functional differentiation was particularly effective in a system in which a magnetic head and a medium slide at high speed.

The lower layer can have a function of controlling surface electric resistance in addition to the function of holding the lubricant. Generally, for controlling the electric resistance, a solid conductive material such as carbon black is often added to the magnetic layer. These not only limit the packing density of the magnetic material but also affect the surface roughness as the magnetic layer becomes thinner. These disadvantages can be eliminated by adding a conductive material to the lower layer.

With the multi-media society, the need for image recording is becoming stronger not only in the industrial world but also in homes. It has the ability to sufficiently meet the demands for function / cost as a medium. The large-capacity medium of the present invention is based on a coated magnetic recording medium with a proven track record, and has excellent long-term reliability and excellent cost performance.

The present invention is achieved for the first time by accumulating various factors as described above and acting synergistically and organically.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION

[Magnetic Layer] In the magnetic recording medium of the present invention, the lower layer and the ultrathin magnetic layer may be provided on only one side or both sides of the support. After applying the lower layer, the upper and lower layers are in a wet state (W / W),
After drying (W / D), the upper magnetic layer can be provided. From the viewpoint of production yield, simultaneous or sequential wet coating is preferable, but in the case of a disc, coating after drying can be used sufficiently. Simultaneous or sequential wet coating (W /
In (W), since the upper layer and the lower layer can be formed simultaneously, a surface treatment step such as a calendering step can be effectively used, and the surface roughness of the upper magnetic layer can be improved even with an ultrathin layer. The coercive force Hc of the magnetic layer needs to be 1800 Oe or more, and the Bm of the metal magnetic powder needs to be 2000 to 5000 G, and the barium ferrite powder needs to have a Bm of 1000 to 3000 G.

[Ferromagnetic Metal Fine Powder] As the ferromagnetic powder used in the upper magnetic layer of the present invention, a ferromagnetic alloy powder containing α-Fe as a main component is preferable. These ferromagnetic powders include Al, Si, S, Sc, Ca, Ti,
V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn,
Sb, Te, Ba, Ta, W, Re, Au, Hg, P
b, Bi, La, Ce, Pr, Nd, P, Co, Mn,
It may contain atoms such as Zn, Ni, Sr, and B. In particular, Al, Si, Ca, Y, Ba, La, Nd,
Preferably, at least one of Co, Ni, and B is contained other than α-Fe, and more preferably, at least one of Co, Y, and Al is contained. The content of Co is preferably from 0 to 40 atomic%, more preferably from 15 to 35 atomic%, more preferably from 20 to 35 atomic% based on Fe. The content of Y is preferably 1.5 atomic% to 12 atomic%, more preferably 3 atomic% to 10 atomic%, and still more preferably 4 atomic%.
Not less than 9 atomic%. Al is 1.5 atomic% or more and 12
Atomic% or less, more preferably 3 atomic% or more and 10 atomic% or less, more preferably 4 atomic% or more and 9 atomic%.
It is as follows. These ferromagnetic powders may be preliminarily treated with a dispersant, a lubricant, a surfactant, an antistatic agent, and the like before dispersion before dispersion. Specifically, JP-B-44-14090, JP-B-45-18372, JP-B-47-22062, JP-B-47-22513,
JP-B-46-28466, JP-B-46-38755
No., JP-B-47-4286, JP-B-47-12422
No., JP-B-47-17284, JP-B-47-1850
No. 9, JP-B-47-18573, JP-B-39-103
07, Japanese Patent Publication No. 46-39639, U.S. Pat.
No. 6215, No. 3031341, No. 3100194
Nos. 3,242,005 and 3,389,014.

The ferromagnetic alloy fine powder may contain a small amount of hydroxide or oxide. A ferromagnetic alloy fine powder obtained by a known production method can be used, and the following method can be used. A method of reducing a complex organic acid salt (mainly oxalate) with a reducing gas such as hydrogen, a method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe—Co particles, Thermal decomposition method, reduction method by adding reducing agent such as sodium borohydride, hypophosphite or hydrazine to aqueous solution of ferromagnetic metal, reduction of fine powder by evaporating metal in low pressure inert gas And how to get it. The ferromagnetic alloy powder thus obtained is subjected to a known slow oxidation treatment, that is, a method of immersing the powder in an organic solvent and then drying it.
A method of immersing in an organic solvent, sending an oxygen-containing gas to form an oxide film on the surface, and then drying, and a method of forming an oxide film on the surface by adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent Any of these can be used.

The ferromagnetic powder of the magnetic layer of the present invention is subjected to the BET method.
45-80m in terms of specific surface area ^Two/ G, preferred
Or 50-70m^Two/ G. 45m^Two/ G or less
Noise rises, 80m^Two/ G or more gives good surface properties
Unfavorable. Crystal of ferromagnetic powder of magnetic layer of the present invention
The child size is 80-180Å, preferably 100-
180 °, more preferably 110 ° to 175 °. strength
The major axis diameter of the magnetic powder is between 0.01 μm and 0.25 μm
And preferably from 0.03 μm to 0.15 μm.
And more preferably 0.03 μm or more and 0.12 μm or less
It is. The needle ratio of the ferromagnetic powder is preferably 3 or more and 15 or less.
And more preferably 5 or more and 12 or less. Magnetic metal powder
Has a value of 100 to 180 emu / g, preferably 11 emu / g.
0 emu / g to 170 emu / g, more preferably 125 to 16
0 emu / g. The coercive force of the metal powder is 1700 Oe or more 3
500 Oe or less, more preferably 1,800 Oe
Not less than 3000 Oe.

The water content of the ferromagnetic metal powder is 0.01 to 2%.
It is preferred that It is preferable to optimize the water content of the ferromagnetic powder depending on the type of the binder. PH of ferromagnetic powder
Is preferably optimized by the combination with the binder used. The range is from 4 to 12, preferably from 6 to
It is 10. The ferromagnetic powder may be subjected to a surface treatment, if necessary, to be in the form of Al, Si, P, or an oxide thereof. The amount is 0.1 to
When the surface treatment is performed, the adsorption of a lubricant such as a fatty acid becomes 100 mg / m ² or less, which is preferable. The ferromagnetic powder may contain inorganic ions such as soluble Na, Ca, Fe, Ni, and Sr. It is preferable that these are essentially absent, but if they are 200 ppm or less, there is little influence on the characteristics. The ferromagnetic powder used in the present invention preferably has a small number of pores, and the value is preferably 20% by volume.
Or less, more preferably 5% by volume or less. The shape may be any of a needle shape, a rice grain shape, and a spindle shape as long as the characteristics of the particle size described above are satisfied.
The smaller the SFD of the ferromagnetic powder itself, the better.
The following is preferred. It is necessary to reduce the distribution of Hc in the ferromagnetic powder. When the SFD is 0.8 or less, the electromagnetic conversion characteristics are good, the output is high, and the magnetization reversal is sharp and the peak shift is small, which is suitable for high-density digital magnetic recording. In order to reduce the distribution of Hc, there are methods for improving the particle size distribution of goethite and preventing sintering in ferromagnetic metal powder.

[Hexagonal Ferrite Fine Powder] As the hexagonal ferrite contained in the uppermost layer of the present invention, there are barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, and Co substitution. Specific examples include magnetoplumbite-type barium ferrite and strontium ferrite, magnetoplumbite-type ferrite whose particle surface is coated with spinel, and magnetoplumbite-type barium ferrite and strontium ferrite further containing a part of spinel phase. , Other than predetermined atoms, Al, Si, S, Sc, T
i, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, S
n, Sb, Te, Ba, Ta, W, Re, Au, Hg,
Pb, Bi, La, Ce, Pr, Nd, P, Co, M
It may contain atoms such as n, Zn, Ni, Sr, B, Ge, and Nb. Generally, Co-Zn, Co-Ti,
Co-Ti-Zr, Co-Ti-Zn, Ni-Ti-Z
n, Nb-Zn-Co, Sb-Zn-Co, Nb-Zn
And the like can be used. material·
Some production methods contain specific impurities. The particle size is 10 to 200 nm in hexagonal plate diameter, preferably 10 to 200 nm.
To 100 nm, particularly preferably 10 to 80 nm.

In particular, when reproducing with a magnetoresistive head in order to increase the track density, it is necessary to reduce noise, and the plate diameter is preferably 40 nm or less, but if it is 10 nm or less, stable magnetization cannot be expected due to thermal fluctuation. Above 200 nm, noise is high and none of them are suitable for high-density magnetic recording. The plate ratio (plate diameter / plate thickness) is desirably 1 to 15. Preferably 1 to
7 When the plate ratio is small, the filling property in the magnetic layer is increased, which is preferable, but sufficient orientation cannot be obtained. If it is larger than 15, noise increases due to stacking between particles. The specific surface area of this particle size range by the BET method is 1
0 to 200 m ² / g. The specific surface area generally corresponds to an arithmetic calculation value from the particle plate diameter and the plate thickness. The distribution of particle plate diameter and plate thickness is generally preferably as narrow as possible. It is difficult to quantify, but the particle T
The comparison can be made by randomly measuring 500 particles from an EM photograph. In many cases, the distribution is not a normal distribution.
0.1 to 2.0. To sharpen the particle size distribution, make the particle generation reaction system as uniform as possible,
A distribution improvement treatment is also performed on the generated particles. For example, a method of selectively dissolving ultrafine particles in an acid solution is also known. Coercive force Hc measured on magnetic material
Can be created up to about 500 Oe to 5000 Oe. A higher Hc is advantageous for high-density recording, but is limited by the capability of the recording head. In the present invention, Hc is from 1700 Oe to 4000.
Oe, but preferably 1800 Oe or more and 3500
Oe or less. When the saturation magnetization of the head exceeds 1.4 Tesler, it is preferable that the saturation magnetization be 2000 Oe or more. H
c is the particle size (plate diameter / plate thickness), the type and amount of contained elements,
It can be controlled by the substitution site of the element, the particle generation reaction conditions and the like. The saturation magnetization s is 40 emu / g to 80 emu / g. σs
Is preferably higher, but tends to be smaller as the particles become finer. It is well known to combine spinel ferrite with magnetoplumbite ferrite to improve σs, and to select the type of element contained and the amount to be added. It is also possible to use W-type hexagonal ferrite. When dispersing the magnetic material, the surface of the magnetic material particles is also treated with a substance suitable for the dispersion medium and the polymer. As the surface treatment material, an inorganic compound or an organic compound is used. The main compound is S
Compounds such as i, Al, P, etc., various silane coupling agents, and various titanium coupling agents are typical examples. The amount is 0.1 to 10% based on the magnetic material. The pH of the magnetic material is also important for dispersion. Usually, the optimum value is about 4 to 12 depending on the dispersion medium and the polymer, but about 6 to 11 is selected from the chemical stability and storage stability of the medium. Water contained in the magnetic material also affects dispersion. There is an optimum value depending on the dispersion medium and the polymer, but usually 0.01 to 2.0% is selected. As a method of producing hexagonal ferrite, a metal oxide that replaces barium oxide, iron oxide, and iron and a glass-forming substance such as boron oxide are mixed to a desired ferrite composition and then melted.
A glass crystallization method in which a barium ferrite crystal powder is obtained by quenching to form an amorphous body, followed by reheating treatment, followed by washing and pulverization to obtain a barium ferrite crystal powder. A hydrothermal reaction method in which a barium ferrite composition metal salt solution is neutralized with an alkali to remove by-products, heated in a liquid phase at 100 ° C. or higher, washed, dried, and pulverized to obtain barium ferrite crystal powder. The barium ferrite composition metal salt solution is neutralized with an alkali, and after removing by-products, dried, treated at 1100 ° C. or lower, and pulverized to obtain a barium ferrite crystal powder. We do not choose manufacturing method.

[Non-Magnetic Layer] Next, the details of the lower layer will be described. The inorganic powder used in the lower layer of the present invention is a non-magnetic powder, for example, selected from inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. Can be. Examples of the inorganic compound include α-alumina, β-alumina, γ-alumina, θ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, hematite, goethite, corundum, and nitride having an α conversion of 90% or more. Silicon, titanium carbide, titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide,
Boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide and the like are used alone or in combination. Particularly preferred are titanium dioxide, zinc oxide, iron oxide and barium sulfate because of their small particle size distribution and many means for imparting functions, and more preferred are titanium dioxide and α-iron oxide. The particle size of these nonmagnetic powders is preferably 0.005 to 2 μm,
If necessary, non-magnetic powders having different particle sizes can be combined, or even a single non-magnetic powder can have the same effect by broadening the particle size distribution. Particularly preferably, the particle size of the non-magnetic powder is from 0.01 μm to 0.2 μm. In particular, when the nonmagnetic powder is a granular metal oxide, the average particle size is preferably 0.08 μm or less, and when the nonmagnetic powder is a needle-shaped metal oxide, the major axis length is preferably 0.3 μm or less, and 0.2 μm or less. Is more preferred. The tap density is 0.05-2 g / ml, preferably 0.2-1.5 g / ml. The water content of the non-magnetic powder is 0.1 to 5% by weight, preferably 0.2 to 3% by weight, more preferably 0.3 to 1.5% by weight. The pH of the nonmagnetic powder is 2 to 11, but p
H is particularly preferably between 5.5 and 10. The specific surface area of the nonmagnetic powder is 1 to 100 m ² / g, preferably 5 to 80 m ² / g,
More preferably, it is 10 to 70 m ² / g. The crystallite size of the nonmagnetic powder is preferably 0.004 μm to 1 μm,
0.04 μm to 0.1 μm is more preferable. Oil absorption using DBP (dibutyl phthalate) is 5-100ml / 100
g, preferably 10 to 80 ml / 100 g, more preferably 20
６０60 ml / 100 g. Specific gravity is 1 to 12, preferably 3
~ 6. The shape may be any of a needle shape, a spherical shape, a polyhedral shape, and a plate shape. The Mohs' hardness is preferably 4 or more and 10 or less. SA (stearic acid) adsorption of non-magnetic powder is 1
２０20 μmol / m ² , preferably 2-15 μmol / m ² , more preferably 3-8 μmol / m ² . pH 3-6
Preferably between The surface of these non-magnetic powders is surface-treated to obtain Al ₂ O ₃ , SiO ₂ , TiO ₂ , Z
Preferably, rO ₂ , SnO ₂ , Sb ₂ O ₃ , ZnO, and Y ₂ O ₃ are present. Particularly preferred for dispersibility is Al ₂
O ₃ , SiO ₂ , TiO ₂ and ZrO ₂ are preferred, and Al ₂ O ₃ , SiO ₂ and ZrO ₂ are more preferred. These may be used in combination or may be used alone. Further, a co-precipitated surface treatment layer may be used according to the purpose, or a method of first treating with alumina and then treating the surface layer with silica, or vice versa, may be employed. Although the surface treatment layer may be a porous layer depending on the purpose, it is generally preferable that the surface treatment layer be homogeneous and dense.

Specific examples of the non-magnetic powder used for the lower layer of the present invention include Nanotite manufactured by Showa Denko, HIT-100, ZA-G1 manufactured by Sumitomo Chemical, and α-hematite DPN-250 and DPN-250BX manufactured by Toda Kogyo. , DPN-24
5, DPN-270BX, DPN-500BX, DBN
-SA1, DBN-SA3, titanium oxide TT manufactured by Ishihara Sangyo
O-51B, TTO-55A, TTO-55B, TTO
-55C, TTO-55S, TTO-55D, SN-1
00, α hematite E270, E271, E300, E
303, titanium industrial titanium oxide STT-4D, STT
-30D, STT-30, STT-65C, α hematite α-40, MT-100S, MT-100 manufactured by Teika
T, MT-150W, MT-500B, MT-600
B, MT-100F, MT-500HD, FI made by Sakai Chemical
NEX-25, BF-1, BF-10, BF-20, S
TM, Dowa Mining DEFIC-Y, DEFIC-R,
AS2BM and TiO2P25 manufactured by Nippon Aerosil, 100A and 500A manufactured by Ube Industries, and baked products thereof. Particularly preferred non-magnetic powders are titanium dioxide and α
-Iron oxide.

By mixing carbon black in the lower layer, it is possible to lower the surface electric resistance Rs, which is a known effect, to reduce the light transmittance, and to obtain a desired micro Vickers hardness. In addition, it is possible to bring about the effect of storing the lubricant by including carbon black in the lower layer. Examples of carbon black include furnace black for rubber, thermal black for rubber, black for color, acetylene black, and the like. The following characteristics of the carbon black in the lower layer should be optimized depending on the desired effect, and the combined effect may provide more effects.

The specific surface area of the lower carbon black is 10
0 to 500 m ² / g, preferably 150 to 400 m ² / g,
DBP oil absorption is 20-400ml / 100g, preferably 30
４００400 ml / 100 g. The particle size of the carbon black is from 5 m to 80 m, preferably from 10 to 50 m, and more preferably from 10 to 40 m. PH of carbon black
Is preferably 2 to 10, the water content is 0.1 to 10%, and the tap density is 0.1 to 1 g / ml. Car used in the present invention
As a specific example of Bon Black, BL made by Cabot Corporation
ACKPEARLS 2000, 1300, 1000,
900, 800, 880, 700, VULCAN XC
-72, # 3050B, # 3150, manufactured by Mitsubishi Chemical Corporation
B, # 3250B, # 3750B, # 3950B, # 9
50, # 650B, # 970B, # 850B, MA-6
00, MA-230, # 4000, # 4010, CONDUCTEX SC, RA manufactured by Konlon Via Carbon
VEN 8800,8000,7000,5750,5
250, 3500, 2100, 2000, 1800, 1
500, 1255, 1250, and Ketjen Black EC manufactured by Akzo Corporation. Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be used after a part of the surface is graphitized. The carbon black may be dispersed with a binder before adding the carbon black to the paint. These carbon blacks are used in an amount of 50 to the above inorganic powder.
It can be used within a range not exceeding 40% by weight and not exceeding 40% of the total weight of the nonmagnetic layer. These carbon blacks can be used alone or in combination. The carbon black that can be used in the present invention can be referred to, for example, "Carbon Black Handbook" (edited by Carbon Black Association).

In the lower layer, an organic powder is used according to the purpose.
It can also be added. For example, acrylic styrene-based resin powder, benzoguanamine resin powder, melamine-based resin powder, phthalocyanine-based pigments, but also polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, and polyfluoroethylene resin Can be used. The manufacturing method is disclosed in
No. 18,564, and those described in JP-A-60-255827 can be used.

For the lower layer binder resin, lubricant, dispersant, additive, solvent, dispersion method and the like, those of the magnetic layer described below can be applied. In particular, binder resin amount, type, additives,
Known techniques for the magnetic layer can be applied to the amount and type of the dispersant. [Binder] The binder, lubricant, dispersant, additive, solvent, dispersing method, etc. of the magnetic layer, non-magnetic layer and back layer of the present invention can be applied to the magnetic layer, non-magnetic layer and back layer.
In particular, the amount of the binder, the type, the additive, the amount of the dispersant added,
As for the type, a known technique for the magnetic layer can be applied.

As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. As a thermoplastic resin, the glass transition temperature is −100 to 150 ° C., and the number average molecular weight is 1.0.
00 to 200,000, preferably 10,000 to 10
000 and a degree of polymerization of about 50 to 1,000.

Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acuric acid,
Acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene,
There are polymers or copolymers containing butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether, and the like as constituent units, polyurethane resins, and various rubber resins. Examples of the thermosetting resin or the reactive resin include a phenol resin, an epoxy resin, a polyurethane curable resin, a urea resin, a melamine resin, an alkyd resin, an acrylic reaction resin, a formaldehyde resin, a silicone resin,
Epoxy-polyamide resin, mixture of polyester resin and isocyanate prepolymer, polyester polyol
And mixtures of polyurethane and polyisocyanate, and mixtures of polyurethane and polyisocyanate. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. In addition, a known electron beam-curable resin can be used for each layer. These examples and the production method thereof are described in detail in JP-A-62-256219. The above resins can be used alone or in combination, but preferred are vinyl chloride resins,
A combination of at least one selected from vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate vinyl alcohol copolymer, vinyl chloride vinyl acetate maleic anhydride copolymer and a polyurethane resin, or polyisocyanate to these. The combination is given.

As the structure of the polyurethane resin, known materials such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycaprolactone polyurethane can be used. For all of the binders shown here, -COO is required to obtain better dispersibility and durability.
_{M, -SO 3 M, -OSO 3} M, -P = O (OM) 2,
-OP = O (OM) ₂ , where M is a hydrogen atom,
Or alkali metal base), —OH, —NR ₂ , —N ⁺
R ₃ (R is a hydrocarbon group), epoxy group, —SH, —C
It is preferable to use one obtained by introducing at least one or more polar groups selected from N and the like by copolymerization or addition reaction. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g.
And preferably 10 ⁻² to 10 ⁻⁶ mol / g.

Specific examples of these binders used in the present invention include VAGH and VY manufactured by Union Carbide.
HH, VMCH, VAGF, VAGD, VROH, VY
ES, VYNC, VMCC, XYHL, XYSG, PK
HH, PKHJ, PKHC, PKFE, manufactured by Nissin Chemical Co., Ltd., MPR-TA, MPR-TA5, MPR-TAL,
MPR-TSN, MPR-TMF, MPR-TS, MP
R-TM, MPR-TAO, 1000W manufactured by Denki Kagaku,
DX80, DX81, DX82, DX83, 100F
D, ZEON Corporation MR-104, MR-105, MR
110, MR100, MR555, 400X-110
A, Nipporan N2301, N2 manufactured by Nippon Polyurethanes
302, N2304, Pandex T manufactured by Dainippon Ink and Chemicals, Inc.
-5105, T-R3080, T-5201, Burnock D-400, D-210-80, Crisbon 610
9,7209, Toyobo Byron UR8200, UR
8300, UR-8700, RV530, RV280,
Daiferamine 4020, 5020, 5 manufactured by Dainichi Seika
100, 5300, 9020, 9022, 7020, manufactured by Mitsubishi Kasei Co., Ltd., MX5004, Samprene S manufactured by Sanyo Kasei Co., Ltd.
P-150 and Saran F310, F210 manufactured by Asahi Kasei Corporation.

The binder used in the non-magnetic layer and the magnetic layer of the present invention is used in a range of 5 to 50%, preferably 10 to 30% with respect to the non-magnetic powder or the magnetic powder. 5 to 30% when using a vinyl chloride resin, 2 to 20% when using a polyurethane resin, polyisocyanate
It is preferable to use these in combination in the range of 2 to 20%. For example, when head corrosion occurs due to a small amount of dechlorination, it is also possible to use only polyurethane or only polyurethane and isocyanate.
In the present invention, when polyurethane is used, the glass transition temperature is -50 to 150C, preferably 0C to 100C.
° C, breaking elongation is 100-2000%, breaking stress is 0.0
Preferably, the yield point is 5 to 10 kg / mm ² and the yield point is 0.05 to 10 kg / mm ² .

The magnetic recording medium of the present invention has two or more layers. Accordingly, the amount of the binder, the amount of the vinyl chloride resin, the polyurethane resin, the polyisocyanate or the other resin in the binder, the molecular weight of each resin forming the magnetic layer, the amount of the polar group, or the amount described above. It is of course possible to change the physical properties of the resin between the non-magnetic layer and each magnetic layer, if necessary. Rather, it should be optimized for each layer, and a known technique for a multilayer magnetic layer can be applied. For example, when changing the amount of binder in each layer, it is effective to increase the amount of binder in the magnetic layer in order to reduce scratches on the surface of the magnetic layer. Can be made flexible by increasing the amount of binder.

The polyisocyanate used in the present invention includes tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and naphthylene-1. ,
5-diisocyanate, o-toluidine diisocyanate
, Isophorone diisocyanate, triphenylmethane triisocyanate and other isocyanates; products of these isocyanates and polyalcohols; and polyisocyanates formed by condensation of isocyanates. -And the like can be used. Commercially available trade names of these isocyanates include Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate M
R, Millionate MTL, Takeda Pharmaceutical Co., Ltd., Takenate D
-102, Takenet D-110N, Takenet D-2
00, Takenate D-202, manufactured by Sumitomo Bayer, Desmodur L, Desmodur IL, Desmodur N, Desmodur HL, etc. These can be used alone or by utilizing the difference in curing reactivity. Each layer can be used in a combination of two or more.

[Carbon Black, Abrasive] Carbon black used in the magnetic layer of the present invention may be furnace black for rubber, thermal black for rubber, black for color, acetylene black, or the like. . Specific surface area is 5-50
0 m ² / g, DBP oil absorption 10-400 ml / 100
g, particle size 5mμ ~ 300mμ, pH 2 ~ 10, water content 0.1 ~ 10%, tap density 0.1 ~ 1g / cc,
Is preferred. Specific examples of carbon black used in the present invention include BLACKPEAR manufactured by Cabot Corporation.
LS 2000, 1300, 1000, 900, 90
5, 800, 700, VULCAN XC-72, manufactured by Asahi Carbon Co., Ltd., # 80, # 60, # 55, # 50, # 3
5. # 2400B, # 2300, #, manufactured by Mitsubishi Kasei Kogyo Co., Ltd.
900, # 1000 # 30, # 40, # 10B, manufactured by Columbian Carbon, CONDUCTEX SC, RA
VEN 150, 50, 40, 15, RAVEN-MT
-P, manufactured by EC Japan, Ketjen Black EC, and the like. Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be used after a part of the surface is graphitized. Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance. These carbon blacks can be used alone or in combination. When carbon black is used, it is preferably used in an amount of 0.1 to 30% of the amount based on the magnetic substance. Carbon black has functions such as preventing the magnetic layer from being charged, reducing the coefficient of friction, imparting light-shielding properties, and improving film strength.
Depends on Bon Black. Therefore, these carbon blacks used in the present invention are different in type, amount and combination in the upper magnetic layer and the lower non-magnetic layer, and the particle size, oil absorption,
It is, of course, possible to selectively use them according to the purpose based on the above-mentioned various properties such as the electric conductivity and the pH. Rather, each layer should be optimized. Carbon black that can be used in the magnetic layer of the present invention is described in, for example, "Carbon Black Handbook".
The edition of the Carbon Black Association can be referred to.

Examples of the abrasive used in the present invention include α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, and silicon carbide having an α conversion of 90% or more. Silicon titanium car
Known materials mainly having a Mohs hardness of 6 or more, such as a bite, titanium oxide, silicon dioxide, and boron nitride, are used alone or in combination. In addition, a composite of these abrasives (abrasive whose surface has been treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the effect remains unchanged if the main component is 90% or more. The particle size of these abrasives is preferably 0.01 to 2 μm, and in particular, in order to enhance the electromagnetic conversion characteristics, it is preferable that the particle size distribution is narrow. Further, in order to improve the durability, it is possible to combine abrasives having different particle sizes as needed, or to achieve the same effect by widening the particle size distribution even with a single abrasive. The tap density is preferably 0.3 to ² g / cc, the water content is 0.1 to 5%, the pH is 2 to 11, and the specific surface area is preferably 1 to 30 m ² / g. The shape of the abrasive used in the present invention is needle-like, spherical, dice-like,
Although any of these may be used, those having a corner in a part of the shape are preferable because of high abrasiveness. Specifically, AKP- manufactured by Sumitomo Chemical Co., Ltd.
12, AKP-15, AKP-20, AKP-30, A
KP-50, HIT-20, HIT-30, HIT-5
5, HIT-60, HIT-70, HIT-80, HI
T-100, manufactured by Reynolds, ERC-DBM, HP-
DBM, HPS-DBM, manufactured by Fujimi Abrasives, WA10
000, Uemura Industry Co., Ltd., UB20, Nippon Chemical Industry Co., Ltd.,
G-5, Chromex U2, Chromex U1, Toda Kogyo Co., Ltd., TF100, TF140, Ibiden Co., Ltd., Beta Random Ultra Fine, Showa Mining Co., Ltd., B-3, and the like. These abrasives can be added to the nonmagnetic layer as needed. By adding to the non-magnetic layer, the surface shape can be controlled, and the projected state of the abrasive can be controlled. The particle size and amount of the abrasive added to the magnetic layer and the non-magnetic layer should of course be set to optimal values.

[Additives] As additives used in the magnetic layer and the nonmagnetic layer of the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect and the like are used. In particular, in the present invention, the lower layer and / or the magnetic layer need to contain at least a saturated fatty acid, an unsaturated fatty acid, and a saturated or unsaturated fatty acid ester. Saturated fatty acids and unsaturated fatty acids include monobasic fatty acids having 10 to 24 carbon atoms (which may be branched), and saturated or unsaturated fatty acid esters include monobasic fatty acids having 10 to 24 carbon atoms ( Any of monovalent, divalent, trivalent, tetravalent, pentavalent and hexavalent alcohols having 2 to 12 carbon atoms (which may be branched); And fatty acid esters of monoalkyl ethers of alkylene oxide polymers. Additives other than these fatty acids and fatty acid esters include molybdenum disulfide, tungsten graphite disulfide, boron nitride, graphite fluoride, silicone oil, silicone having a polar group, fatty acid modified silicone, and fluorine-containing silicone. , Fluorine-containing alcohols, fluorine-containing esters, polyolefins, polyglycols, alkyl phosphates and alkali metal salts thereof, alkyl sulfates and alkali metal salts thereof, polyphenyl ether, phenyl phosphonic acid, α-naphthyl phosphoric acid, phenyl phosphoric acid, Diphenylphosphoric acid, p-ethylbenzenephosphonic acid, phenylphosphinic acid, aminoquinones, various silane coupling agents, titanium coupling agents, fluorine-containing alkyl sulfates and alkali metal salts thereof, monobasic fatty acids having 10 to 24 carbon atoms A metal salt (which may contain an unsaturated bond or may be branched) (e.g., Li, Na, K, Cu), or a monovalent, divalent, trivalent, tetravalent, pentavalent or pentavalent C22-C22 metal salt. Valent, hexavalent alcohol, (including unsaturated bond,
It may be branched), alkoxy alcohols having 12 to 22 carbon atoms, fatty acid amides having 8 to 22 carbon atoms, aliphatic amines having 8 to 22 carbon atoms, and the like can be used.

Specific examples of these fatty acids include capric acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid and isostearic acid. Can be Esters include butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, butyl myristate, octyl myristate, butoxyethyl stearate, butoxydiethyl stearate, 2-ethylhexyl stearate, and 2-octyldodecyl palmitate. 2-hexyl decyl palmitate, isohexadecyl stearate, oleyl oleate, dodecyl stearate, tridecyl stearate, oleyl erucate, neopentyl glycol didecanoate, ethylene glycol dioleyl, oleyl alcohol for alcohols , Stearyl alcohol, lauryl alcohol and the like.
Also, nonionic surfactants such as alkylene oxides, glycerin, glycidols, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives,
Heterocycles, cationic surfactants such as phosphoniums or sulfoniums, carboxylic acids, sulfonic acids, phosphoric acids,
Anionic surfactants containing an acidic group such as a sulfate group or a phosphate group, amphoteric surfactants such as amino acids, aminosulfonic acids, sulfuric acid or phosphates of amino alcohol, and alkylbedine type are also included. Can be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc. are always 100%
It is not pure and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, etc. in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less.

These lubricants and surfactants used in the present invention have different physical actions, respectively.
The type, amount, and combination ratio of the lubricant that produces a synergistic effect should be optimally determined according to the purpose.
To control leaching to the surface using fatty acids having different melting points in the non-magnetic layer and magnetic layer, to control leaching to the surface using esters having different boiling points, melting points and polarities, and to adjust the amount of surfactant It can be considered to improve the stability of coating and to improve the lubricating effect by increasing the amount of the lubricant added in the intermediate layer, and it is needless to say that the present invention is not limited to the examples shown here. Generally, the total amount of the lubricant is 0.1% to 50%, preferably 2% to 25%, based on the magnetic powder or nonmagnetic powder.
It is selected in the range of%.

All or a part of the additives used in the present invention may be added at any step in the production of magnetic and non-magnetic paints. There are a case where it is added in a kneading step using a body, a binder and a solvent, a case where it is added in a dispersion step, a case where it is added after dispersion, and a case where it is added just before coating. In some cases, the purpose may be achieved by applying a part or all of the additive simultaneously or sequentially after applying the magnetic layer according to the purpose. Depending on the purpose, a lubricant may be applied to the surface of the magnetic layer after calendering or after slitting. Known organic solvents can be used in the present invention.
The solvent described in 453 can be used.

[Layer Structure] The thickness structure of the magnetic recording medium of the present invention is as follows.
0 μm. The nonmagnetic support of the computer tape is 3.0 to 6.5 μm (preferably 3.0 to 6.0 μm).
μm, and more preferably, a thickness in the range of 4.0 to 5.5 μm).

An undercoat layer for improving adhesion may be provided between the nonmagnetic flexible support and the nonmagnetic layer or magnetic layer. The thickness of the undercoat layer is 0.01 to 0.5 μm, preferably 0.02 to 0.5 μm. The present invention may be a double-sided magnetic layer disk-shaped medium in which a nonmagnetic layer and a magnetic layer are usually provided on both sides of the support, or may be provided on only one side. In this case, a back coat layer may be provided on the side opposite to the non-magnetic layer and the magnetic layer in order to obtain effects such as antistatic and curl correction. This thickness is 0.1 to 4 μm, preferably 0.3 to 2.0 μm. Known undercoat layers and backcoat layers can be used.

The thickness of the magnetic layer of the medium of the present invention is optimized according to the saturation magnetization of the head used, the head gap length, and the band of the recording signal.
Not less than 0.25 μm, preferably 0.05 μm
It is not less than 0.20 μm. The magnetic layer may be separated into two or more layers having different magnetic properties, and a known configuration relating to a multilayer magnetic layer can be applied.

The thickness of the nonmagnetic layer which is the lower layer of the medium according to the present invention is 0.2 μm or more and 5.0 μm or less, preferably 0.1 μm or less.
3 μm or more and 3.0 μm or less, more preferably 1.0 μm
m or more and 2.5 μm or less. The lower layer of the medium of the present invention exerts its effect as long as it is substantially a non-magnetic layer. Needless to say, the configuration can be regarded as substantially the same as that of the present invention. Substantially a nonmagnetic layer means that the lower layer has a residual magnetic flux density of 100 G or less or a coercive force of 100 Oe or less, and preferably has no residual magnetic flux density and coercive force.

[Backcoat Layer] Generally, magnetic tapes for recording computer data are required to have a higher repetitive running property than video tapes and audio tapes. In order to maintain such high running durability, the back coat layer preferably contains carbon black and inorganic powder.

The carbon black is preferably used in combination of two kinds having different average particle sizes. In this case, fine carbon black having an average particle size of 10 to 20 μm and an average particle size of 230 to 30
It is preferable to use a combination of 0 μm coarse carbon black. In general, the surface electric resistance of the back coat layer can be set low and the light transmittance can be set low by the addition of the fine carbon black as described above. Some magnetic recording devices use the light transmittance of the tape and use it as an operation signal. In such a case, the addition of fine carbon black is particularly effective. In addition, fine carbon black is generally excellent in holding power of a liquid lubricant, and contributes to reduction of a friction coefficient when used in combination with a lubricant. On the other hand, when the particle size is 230 to 30
Coarse-particle carbon black having a particle size of 0 μm has a function as a solid lubricant, and forms fine protrusions on the surface of the back layer, thereby reducing the contact area and contributing to a reduction in the friction coefficient. However, the coarse-grained carbon black has a drawback that in a severe running system, the tape slides easily to drop off from the back coat layer, leading to an increase in the error ratio.

Specific products of the particulate carbon black include the following. RAVE
N2000B (18mμ), RAVEN 1500B (1
7mμ) (all manufactured by Columbia Carbon Co., Ltd.), BP80
0 (17mμ) (Cabot Corporation), PRINTENTEX
90 (14mμ), PRINTEX95 (15mμ),
PRINTEX85 (16mμ), PRINTEX75
(17 mμ) (all manufactured by Degussa), # 3950 (16
mμ) (manufactured by Mitsubishi Chemical Corporation).

Specific examples of commercial products of coarse particle carbon black include thermal black (270 mμ) (manufactured by Khancarb) and RAVEN MTP (275 mμ).
(Made by Columbia Carbon Co., Ltd.).

In the case of using two types having different average particle sizes in the back coat layer, 10 to 20 μm
Is preferably in the range of 98: 2 to 75:25, and more preferably 95: 5. ~ 85: 15.

The content of carbon black in the back coat layer (when two types are used, the total amount thereof) is usually in the range of 30 to 80 parts by weight with respect to 100 parts by weight of the binder. Preferably, it is in the range of 45 to 65 parts by weight.

It is preferable to use two kinds of inorganic powders having different hardnesses in combination. Specifically, Mohs hardness 3 ~
It is preferable to use a 4.5 soft inorganic powder and a 5 to 9 Mohs hardness hard inorganic powder. Mohs hardness is 3-4.
By adding the soft inorganic powder of No. 5, the friction coefficient can be stabilized by repeated running. Further, with the hardness in this range, the sliding guide pole is not cut off. The average particle size of this inorganic powder is 30 to 50.
It is preferably in the range of mμ.

Examples of the soft inorganic powder having a Mohs' hardness of 3 to 4.5 include calcium sulfate, calcium carbonate, calcium silicate, barium sulfate, magnesium carbonate, zinc carbonate, and zinc oxide. They are,
They can be used alone or in combination of two or more. Among these, calcium carbonate is particularly preferred.

The content of the soft inorganic powder in the back coat layer is from 10 to 14 with respect to 100 parts by weight of carbon black.
It is preferably in the range of 0 parts by weight, more preferably 35 to 100 parts by weight.

The addition of the hard inorganic powder having a Mohs hardness of 5 to 9 enhances the strength of the back coat layer and improves the running durability. When these inorganic powders are used together with carbon black or the above-mentioned soft inorganic powders, they are less deteriorated even in repeated sliding and form a strong backcoat layer. In addition, the addition of the inorganic powder provides an appropriate polishing force, and reduces the adhesion of shavings to the tape guide pole and the like. In particular, when used in combination with a soft inorganic powder (among others, calcium carbonate), the sliding characteristics with respect to a guide pole having a rough surface are improved, and the friction coefficient of the back coat layer can be stabilized.

The hard inorganic powder has an average particle size of 8
0 to 250 mμ (more preferably, 100 to 210 m
μ).

Examples of the hard inorganic powder having a Mohs hardness of 5 to 9 include α-iron oxide, α-alumina, and chromium oxide (Cr ₂ O ₃ ). These powders may be used alone or in combination. Of these, α-iron oxide or α-alumina is preferred. The content of the hard inorganic powder is usually 3 to 30 parts by weight based on 100 parts by weight of carbon black,
Preferably, it is 3 to 20 parts by weight.

When the soft inorganic powder and the hard inorganic powder are used in combination in the back coat layer, the difference in hardness between the soft inorganic powder and the hard inorganic powder is 2 or more (more preferably 2.5 or more, particularly preferably It is preferable to select and use a soft inorganic powder and a hard inorganic powder as in (3).

It is preferable that the back coat layer contains the two types of inorganic powders having different specific Mohs hardnesses, each having the specific average particle size, and the two types of carbon black having different average particle sizes. Especially,
In this combination, it is preferable that calcium carbonate is contained as the soft inorganic powder.

The back coat layer may contain a lubricant. The lubricant can be appropriately selected from the above-mentioned lubricants that can be used for the nonmagnetic layer or the magnetic layer. In the back coat layer, the lubricant is usually added in a range of 1 to 5 parts by weight based on 100 parts by weight of the binder. [Support] Non-magnetic supports used in the present invention include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulostriacetate, polycarbonate, polyamide, polyimide and polyamideimide. And known films such as polysulfone, polyaramid, aromatic polyamide, and polybenzoxazole. Polyethylene naphthalene
It is preferable to use a high-strength support such as polyamide or polyamide. If necessary, a laminated type support as disclosed in JP-A-3-224127 can be used to change the surface roughness of the magnetic surface and the base surface. These supports may be subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, or the like in advance.
In addition, an aluminum or glass substrate can be used as the support of the present invention.

To achieve the object of the present invention, the surface roughness meter TOPO-3D manufactured by WYKO is used as a non-magnetic support.
The center plane average surface roughness measured by the irau method has an SRa of 8.0 nm or less, preferably 4.0 nm or less, and more preferably 2.0 nm or less. It is preferable that these non-magnetic supports not only have a small center plane average surface roughness but also have no coarse protrusions of 0.5 μm or more. The surface roughness can be freely controlled by the size and amount of the filler added to the support as required. Examples of these fillers include oxides and carbonates such as Ca, Si, and Ti, and organic fine powders such as acryl. The maximum height SRmax of the support is 1 μm or less, and the ten-point average roughness SRz is 0.5 μm.
Hereinafter, the center plane peak height SRp is 0.5 μm or less, the center plane trough depth SRv is 0.5 μm or less, and the center plane area ratio SSr is 10 μm or less.
% Or more and 90% or less, and the average wavelength Sλa is 5 μm or more and 30% or less.
It is preferably 0 μm or less. In order to obtain desired electromagnetic conversion characteristics and durability, the surface projection distribution of these supports can be arbitrarily controlled by a filler.
Can be controlled in the range of 0 to 2000 pieces per 0.1 mm ² .

The non-magnetic support used in the present invention, F-5
The value is preferably 5 to 50 kg / mm ² , and 100
The heat shrinkage at 30 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage at 80 ° C. for 30 minutes is preferably 1% or less, more preferably 0.5% or less. . Breaking strength is 5-100 kg / mm ² , elastic modulus is 100-
2000 kg / mm ² is preferred. Temperature expansion coefficient is 10 ^-4 or more
10 ⁻⁸ / ° C., preferably 10 ⁻⁵ to 10 ⁻⁶ / ° C. The humidity expansion coefficient is 10 ⁻⁴ / RH% or less, preferably 10 ⁻⁵ / RH% or less. These thermal properties, dimensional properties,
It is preferable that the mechanical strength characteristics be substantially equal to each other in the in-plane direction of the support with a difference within 10%.

[Production Method] The step of producing the magnetic coating material of the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Each step may be divided into two or more steps. All the raw materials such as magnetic powder, non-magnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant and solvent used in the present invention may be added at the beginning or during any step. Further, individual raw materials may be added in two or more steps in a divided manner. For example, polyurethane may be divided and supplied in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, a conventionally known manufacturing technique can be used as a part of the steps. In the kneading step, it is preferable to use one having a strong kneading force, such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. When a kneader is used, all or a part of the magnetic powder or the non-magnetic powder and the binder (30% of the total binder) is used.
% Or more) and 15 parts per 100 parts of magnetic powder.
The kneading process is performed in a range of up to 500 parts. Details of these kneading processes are described in JP-A-1-106338 and JP-A-1-106338.
79274. Glass beads can be used to disperse the magnetic layer solution and the non-magnetic layer solution, but zirconia beads, titania beads, and steel beads, which are high-density dispersion media, are preferable. The particle size and the filling rate of these dispersion media are optimized and used. A well-known disperser can be used.

When a magnetic recording medium having a multilayer structure is applied in the present invention, the following method is preferably used. First, a lower layer is first applied by a gravure coating, a roll coating, a blade coating, an extrusion coating device, etc., which are generally used in the application of a magnetic paint. Showa 60-238
179, a method of applying an upper layer using a support-pressing-type extrusion coating apparatus disclosed in JP-A-2-265672. Second, JP-A-63-88080 and JP-A-2-
No. 17971, Japanese Patent Application Laid-Open No. 2-265672 discloses a method in which upper and lower layers are coated almost simultaneously by one coating head having two built-in coating liquid passage slits. A third method is to apply the upper and lower layers almost simultaneously using an extrusion coating apparatus with a backup roll disclosed in Japanese Patent Application Laid-Open No. 2-174965. Incidentally, in order to prevent the electromagnetic conversion characteristics and the like of the magnetic recording medium from deteriorating due to the aggregation of the magnetic particles, JP-A-62-95174 and JP-A-1-236968 have been proposed.
It is desirable to apply shear to the coating liquid inside the coating head by a method as disclosed in US Pat. Further, the viscosity of the coating liquid must satisfy the numerical range disclosed in JP-A-3-8471. In order to realize the structure of the present invention, it is of course possible to use a sequential multi-layer coating in which a lower layer is applied and dried, and then a magnetic layer is provided thereon, and the effect of the present invention is not lost. However, in order to reduce coating defects and improve quality such as dropout, it is preferable to use the above-described simultaneous multilayer coating.

In the case of a disk, a sufficient isotropic orientation may be obtained even without orientation, without using an orientation device. It is preferable to use a known random alignment device. In the case of the ferromagnetic metal fine powder, isotropic orientation is generally preferred to be in-plane two-dimensional random,
Three-dimensional randomness can be obtained by adding a vertical component. In the case of hexagonal ferrite, three-dimensional randomness in the in-plane and vertical directions generally tends to occur, but in-plane two-dimensional randomness is also possible. In addition, isotropic magnetic characteristics can be imparted in the circumferential direction by using a known method such as a different polarity opposed magnet and making the magnets vertically oriented. In particular, when performing high-density recording, vertical alignment is preferable. In addition, circumferential orientation may be performed using spin coating.

In the case of a magnetic tape, it is oriented in the longitudinal direction using a cobalt magnet or a solenoid. It is preferable that the drying position of the coating film can be controlled by controlling the temperature of the drying air, the amount of air, and the coating speed.
The temperature of the drying air is preferably 60 ° C. or more at 000 m / min, and an appropriate preliminary drying can be carried out before entering the magnet zone.

A calendering roll is treated with a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimideamide or a metal roll.
In particular, in the case of forming a double-sided magnetic layer, it is preferable to perform the treatment with metal rolls. The processing temperature is preferably 50 ° C. or higher,
More preferably, the temperature is 100 ° C. or higher. The linear pressure is preferably at least 200 kg / cm, more preferably at least 300 kg / cm.

[Physical Characteristics] The saturation magnetic flux density of the magnetic layer of the magnetic recording medium according to the present invention is 2,000 G or more and 5,000 G or less when ferromagnetic metal fine powder is used, and 1000 G or more and 3000 G or less when hexagonal ferrite is used. . The coercive force Hc and Hr are not less than 1500 Oe and not more than 5000 Oe, preferably from 1700 Oe to 3000 Oe.
e or less. The distribution of coercive force is preferably narrow, and SF
D and SFDr are preferably 0.6 or less. Squareness ratio is 2
0.55 or more and 0.67 or less in the case of dimensional random, preferably 0.58 or more and 0.64 or less. In the case of three-dimensional random, it is preferably 0.45 or more and 0.55 or less. It is 0.6 or more, preferably 0.7 or more in the vertical direction, and 0.7 or more, preferably 0.8 or more when demagnetizing field correction is performed. The orientation ratio is preferably 0.8 or more for both two-dimensional random and three-dimensional random. In the case of two-dimensional randomness, it is preferable that the squareness ratio in the vertical direction, Br, Hc, and Hr be within 0.1 to 0.5 times the in-plane direction.

In the case of a magnetic tape, the squareness ratio is 0.7 or more,
Preferably it is 0.8 or more. The coefficient of friction of the magnetic recording medium of the present invention with respect to the head is 0.5 or less, preferably 0.3 or less, in the temperature range of -10 ° C. to 40 ° C. and the humidity of 0% to 95%. ^Four
-10 to ¹² ohms / sq, charged potential from -500V to + 500V
Is preferably within. Preferably 100 to 2,000 kg / mm ² in elastic modulus plane directions at 0.5% elongation of the magnetic layer, the breaking strength is preferably 10 to 70 kg / mm ^2, the modulus of elasticity of the magnetic recording medium is plane directions And preferably 100 to 1500 kg /
mm ² , residual elongation is preferably 0.5% or less, heat shrinkage at any temperature of 100 ° C. or less is preferably 1% or less,
More preferably, it is 0.5% or less, most preferably 0.1% or less. Glass transition temperature of magnetic layer (110H
The maximum point of the loss elastic modulus of the dynamic viscoelasticity measurement measured in z) is 5
The temperature is preferably from 0 ° C to 120 ° C, and that of the lower nonmagnetic layer is preferably from 0 ° C to 100 ° C. The loss modulus is 1 × 10 ⁸
８8 × 10 ⁹ dyne / cm ² , and the loss tangent is preferably 0.2 or less. If the loss tangent is too large, adhesion failure is likely to occur. It is preferable that these thermal characteristics and mechanical characteristics are substantially equal within 10% in each direction in the plane of the medium. The residual solvent contained in the magnetic layer is preferably 100 mg / m ² or less, more preferably 10 mg / m 2
² or less. The porosity of the coating layer is preferably 30% by volume or less, more preferably 20% by volume or less, for both the nonmagnetic lower layer and the magnetic layer. The porosity is preferably small in order to achieve high output, but it may be better to secure a certain value depending on the purpose. For example, in a disk medium in which repeated use is emphasized, a larger porosity is often preferable in running durability.

Surface roughness tester TOP manufactured by WYCO of the magnetic layer
Center plane surface roughness Ra measured by the Mirau method of O-3D
Is 4.0 nm or less, preferably 3.8 nm or less, and more preferably 3.5 nm or less. Maximum height SRmax of magnetic layer
Is 0.5 μm or less, the ten-point average roughness SRz is 0.3 μm or less, the center plane peak height SRp is 0.3 μm or less, the center plane trough depth SRv is 0.3 μm or less, and the center plane area ratio SSr is 20% or more. , 80% or less, average wavelength Sλa is 5 μm or more, 300 μm
m or less is preferable. The surface protrusions of the magnetic layer can be arbitrarily set in a range of 0 to 2000 with a size of 0.01 μm to 1 μm, and it is preferable to optimize the electromagnetic conversion characteristics and the friction coefficient. . These can be easily controlled by controlling the surface properties by the filler of the support, the particle size and amount of the powder to be added to the magnetic layer, and the roll surface shape of the calendar treatment. The curl is preferably within ± 3 mm.

When the magnetic recording medium of the present invention has a nonmagnetic layer and a magnetic layer, it is easily presumed that the physical properties of the nonmagnetic layer and the magnetic layer can be changed according to the purpose. For example, the elastic modulus of the magnetic layer is increased to improve running durability, and at the same time, the elastic modulus of the non-magnetic layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head.

[0089]

EXAMPLES <Preparation of paint> Magnetic paint ML-1 (using needle-like magnetic powder) Ferromagnetic metal fine powder: 100 parts of M-1 Composition: Co / Fe (atomic ratio) 30% Hc2550Oe, specific surface area 55 m ² / g, σs140 emu / g Crystallite size 120 °, major axis length 0.048 μm, needle ratio 4 Sintering inhibitor Al compound (Al / Fe atomic ratio 8%) Y compound (Y / Fe atomic ratio 6%) Vinyl chloride Polymer MR110 (manufactured by Zeon Corporation) 12 parts Polyurethane resin UR8200 (manufactured by Toyobo Co., Ltd.) 3 parts α-alumina HIT55 (manufactured by Sumitomo Chemical Co., Ltd.) 10 parts Carbon black # 50 (manufactured by Asahi Carbon Co., Ltd.) 5 parts Phenylphosphonic acid 3 Part Butyl stearate 10 parts Butoxyethyl stearate 5 parts Isohexadecyl stearate 3 parts Stearic acid 2 parts Methyl ethyl ketone 180 parts Cyclohexano 180 parts Magnetic paint ML-2 (using needle-shaped magnetic powder) Ferromagnetic metal fine powder: 100 parts M-2 Composition: Co / Fe (atomic ratio) 30% Hc2360 Oe, specific surface area 49 m ² / g, σs 146 emu / g crystal Element size 170 mm, major axis length 0.100 μm, needle ratio 6, SFD 0.51 sintering inhibitor Al compound (Al / Fe atomic ratio 5%) pH 9.4 Y compound (Y / Fe atomic ratio 5%) Vinyl chloride copolymer MR110 (manufactured by Zeon Corporation) 10 parts Polyurethane resin UR5500 (manufactured by Toyobo) 4 parts α-alumina HIT70 (manufactured by Sumitomo Chemical) 10 parts Carbon black # 50 (manufactured by Asahi Carbon Co.) 1 part Phenyl Phosphonic acid 3 parts Oleic acid 1 part Stearic acid 0.6 parts Ethylene glycoldioleyl 12 parts Methyl ethyl ketone 180 parts Cyclohexanone 180 parts Magnetic paint M -3 (acicular magnetic powder used: Comparative Example) ferromagnetic metal powder: M-3 Composition / Fe: Ni = 96: 4 100 parts Hc1600Oe, a specific surface area of 45 m ² / g Crystallite size 220Å, σs135emu / g average major axis Diameter 0.20 μm, needle ratio 9 Vinyl chloride copolymer MR110 (Nippon Zeon) 12 parts Polyurethane resin UR-8600 (Toyobo) 5 parts α-alumina (particle diameter 0.65 μm) 2 parts Chromium oxide (particles) Size: 0.35 μm) 15 parts Carbon black (particle size: 0.03 μm) 2 parts Carbon black (particle size: 0.3 μm) 9 parts Isohexadecyl stearate 4 parts n-butyl stearate 4 parts Butoxyethyl stearate 4 parts Oleic acid 1 part Stearic acid 1 part Methyl ethyl ketone 300 parts Magnetic paint ML-4 (using plate-like magnetic powder) 100 parts Barium ferrite magnetic powder: M-4 to Ba molar ratio composition: Fe 9.10, Co 0.20, Zn 0.77 Hc 2500 Oe, specific surface area 50 m ² / g, σs 58 emu / g plate diameter 35 nm, plate ratio 4 vinyl chloride co-weight Combined MR110 (manufactured by Zeon Corporation) 12 parts Polyurethane resin UR8200 (manufactured by Toyobo) 3 parts α-alumina HIT55 (manufactured by Sumitomo Chemical) 10 parts Carbon black # 50 (manufactured by Asahi Carbon) 5 parts Phenylphosphonic acid 3 parts Butyl stearate 10 parts Butoxyethyl stearate 5 parts Isohexadecyl stearate 3 parts Stearic acid 2 parts Methyl ethyl ketone 125 parts Cyclohexanone 125 parts Magnetic paint ML-5 (using plate-like magnetic powder) Barium ferrite magnetic powder: M-5 100 parts Mo composition ratio to Ba: Fe 9.10, Co 0.20, Zn 0. 7 Hc2500Oe, a specific surface area of ^{50m 2 / g, σs 58emu /} g plate size 35 nm, plate ratio 2.5 vinyl copolymer chloride polymer MR 110 (Nippon Zeon Co., Ltd.) 10 parts Polyurethane resin UR5500 (manufactured by Toyobo Co., Ltd.) 4 parts α-alumina HIT55 (manufactured by Sumitomo Chemical Co., Ltd.) 10 parts # 50 (manufactured by Asahi Carbon Co., Ltd.) 1 part Phenylphosphonic acid 3 parts Oleic acid 1 part Stearic acid 0.6 part Ethylene glycol-dioldioleyl 16 parts Methyl ethyl ketone 180 parts Cyclohexanone 180 parts Nonmagnetic paint NU-1 (using spherical inorganic powder) Non-magnetic powder TiO ₂ crystalline rutile 80 parts Average primary particle diameter 0.035 μm, specific surface area by BET method 40 m ² / g pH 7 TiO ₂ content 90% or more, DBP oil absorption 27~38g / 100g, Al ₂ O ₃ is with respect to the entire particles to the surface 8 wt% presence mosquitoes - carbon black conductance SCX-U (manufactured by Columbian Carbon Co., Ltd.) 20 parts Vinyl chloride copolymer MR110 (manufactured by Nippon Zeon) 12 parts Polyurethane resin UR8200 (manufactured by Toyobo Co., Ltd.) 5 parts Phenylphosphonic acid 4 parts butyl stearate 10 parts butoxyethyl steer Rate 5 parts Isohexadecyl stearate 2 parts Stearic acid 3 parts Methyl ethyl ketone / cyclohexanone (8/2 mixed solvent) 250 parts Nonmagnetic paint NU-2 (using spherical inorganic powder) Nonmagnetic powder TiO ₂ crystalline rutile 100 parts Average Primary particle diameter 0.035 μm, specific surface area by BET method 40 m ² / g pH 7 TiO ₂ content 90% or more, DBP oil absorption 27-38 g / 100 g, Al ₂ O ₃ and SiO _{2 on the} surface Ketjen Black EC (AKUZO NOBEL) 13 parts Average primary particle diameter: 30mμ DBP absorption The amount: 350 ml / 100 g pH: 9.5 BET specific surface area: 950 meters ² / g Volatile content: 1.0% Vinyl chloride copolymer MR 110 (manufactured by Nippon Zeon Co., Ltd.) 16 parts Polyurethane resin UR8200 (manufactured by Toyobo Co., Ltd.) 6 Part Phenylphosphonic acid 4 parts Ethylene glycol-dioleoleyl 16 parts Oleic acid 1 part Stearic acid 0.8 parts Methyl ethyl ketone / cyclohexanone (8/2 mixed solvent) 250 parts Nonmagnetic paint NU-3 (using spherical inorganic powder: comparative example) Magnetic powder TiO ₂ crystalline rutile 75 parts Average primary particle diameter 0.035 μm, Specific surface area 40 m ² / g pH 7 TiO ₂ content 90% or more, DBP oil absorption 27-38 g / 100 g, Al ₂ O _{3 on the} surface, SiO ₂ is present in mosquitoes - carbon black Ketchen black EC 10 parts of α-alumina AKP-15 (manufactured by Sumitomo Chemical Co., Ltd.) average Particle size: 0.65 μm 15 parts Vinyl chloride copolymer MR110 (manufactured by Nippon Zeon) 12 parts Polyurethane resin UR8600 (manufactured by Toyobo Co., Ltd.) 5 parts Isohexadecyl stearate 4 parts n-butyl stearate 4 parts Butoxyethyl stearate 4 parts Oleic acid 1 part Stearic acid 1 part Methyl ethyl ketone 300 parts Non-magnetic paint NU-4 (using needle-like inorganic powder) Non-magnetic powder α-Fe ₂ O ₃ hematite 80 parts Long axis length 0.15 μm, ratio by BET method Surface area 50 m ² / g pH 9 Al ₂ O ₃ is present on the surface in an amount of 8% by weight with respect to the whole particles Carbon black Conductex SC-U (manufactured by Columbian Carbon Co., Ltd.) 20 parts Vinyl chloride copolymer MR110 (Zeon Corporation) 12 parts Polyurethane resin UR8200 (manufactured by Toyobo) 5 parts Phenylphosphonic acid 4 parts Stearate 10 parts Butoxyethyl stearate 5 parts Isohexadecyl stearate 2 parts Stearic acid 3 parts Methyl ethyl ketone / cyclohexanone (8/2 mixed solvent) 250 parts Non-magnetic paint NU-5 (using needle-like inorganic powder) Non-magnetic powder α-Fe ₂ O ₃ hematite 100 parts Long axis length 0.15 μm, BET specific surface area 50 m ² / g pH 9, Carbon black # 3250B (Al ₂ O _{3 present on the} surface 8% by weight based on the whole particles) 18 parts Vinyl chloride copolymer MR104 (manufactured by Zeon Corporation) 15 parts Polyurethane resin UR5500 (manufactured by Toyobo) 7 parts Phenylphosphonic acid 4 parts Ethylene glycol-dioleoleyl 16 parts Oleic acid 1.3 parts Stearic acid 0.8 parts Methyl ethyl ketone / cyclohexanone (8/2 mixed solvent) 250 parts Information: (disk W / W) each paint above 10, the components two - were were kneaded by Da, dispersed in a sand mill. To the resulting dispersion, 10 parts of polyisocyanate was added to the coating liquid for the non-magnetic layer, 10 parts to the coating liquid for the magnetic layer, and 40 parts of cyclohexanone was added to each. A filter having an average pore diameter of 1 μm was added. And a coating solution for forming a nonmagnetic layer and a coating solution for forming a magnetic layer were respectively prepared.

The obtained non-magnetic layer coating solution was applied to a thickness of 62 μm so that the thickness after drying was 1.5 μm, and immediately thereafter, the thickness of the magnetic layer was 0.15 μm thereon. At the same time, a multi-layer coating is performed on a polyethylene terephthalate support having a center plane average surface roughness of 3 nm, and while both layers are still in a wet state, a frequency of 50 Hz, a magnetic field strength of 250 Gauss and a frequency of 50 Hz and 120 Gauss are applied. After passing through two AC magnetic field generators and performing random orientation treatment and drying, the temperature is 90 ° C and the linear pressure is 300 with a 7-stage calendar.
After processing at 3.7 kg / cm and punching to 3.7 inches and subjecting to surface polishing, it was placed in a 3.7-inch cartridge (zip-disk cartridge manufactured by Iomega, USA) with a liner installed inside, 3.7 additional mechanical parts
An inch floppy disk was obtained. Some of the samples were subjected to longitudinal orientation using a 4000 G homopolar opposing Co magnet before randomizing orientation treatment.

In this case, it is preferable to increase the frequency and the magnetic field strength of the AC magnetic field generator so that sufficient randomization is finally performed, whereby an orientation ratio of 98% or more can be obtained. When a barium ferrite magnetic material is used, vertical alignment can be performed in addition to the above-described alignment method. Also, if necessary, after punching into a disk shape, heat treatment at high temperature (normally 50 ° C to 90 ° C)
May be performed to accelerate the curing treatment of the coating layer, to perform burnishing treatment with a polishing tape, and to perform post-treatment such as shaving projections on the surface. Production method 2 (Computer tape: W / W) After kneading each component with a kneader,
It was dispersed using a sand mill. To the obtained dispersion, 2.5 parts of polyisocyanate is added to the coating solution for the non-magnetic layer, 3 parts to the coating solution for the magnetic layer, and 40 parts of cyclohexanone is added to each, to have an average pore diameter of 1 μm. The solution was filtered using a filter to prepare a coating solution for forming a nonmagnetic layer and a coating solution for forming a magnetic layer.

The obtained coating solution for the non-magnetic layer was applied to a thickness of 4 μm so that the thickness after drying became 1.7 μm, and immediately thereafter, the thickness of the magnetic layer became 0.15 μm. .4μ
m and an aramid support (trade name: MICRON) having a center plane average surface roughness of 2 nm. Orientation was carried out by the holding solenoid. After drying, 200 m / min. Speed / 85 ° C./min.
After that, the back layer having a thickness of 0.5 μm (carbon black average particle size: 17 μm 100 parts,
Calcium carbonate average particle size: 40 mμ 80 parts,
α-alumina Average particle size: 200 μm 5 parts were dispersed in nitrocellulose resin, polyurethane resin and polyisocyanate). It is slit to a width of 3.8 mm, and the nonwoven fabric and razor blade are attached to a device having a slitting device to feed and take up the slit product so that the nonwoven fabric and the razor blade are pressed against the magnetic surface. After cleaning, the obtained magnetic tape was incorporated into a DDS cartridge. Production Method 3 (Disk: W / D) For each of the above 10 paints, each component was kneaded with a kneader, and then dispersed using a sand mill. In the obtained dispersion, polyisocyanate was added to the coating liquid for the non-magnetic layer.
0 parts, 10 parts of the coating solution for the magnetic layer, and 40 parts of cyclohexanone were added to each, and the mixture was filtered using a filter having an average pore size of 1 μm. Were adjusted respectively.

The obtained coating solution for the nonmagnetic layer was coated on a polyethylene terephthalate support having a thickness of 62 μm and a center plane average surface roughness of 3 nm so that the thickness after drying would be 1.5 μm. Once dried and calendered, a magnetic layer is applied thereon by a blade method so that the thickness of the magnetic layer is 0.15 μm, and the frequency is 50 Hz, the magnetic field strength is 250 Gauss, and the frequency is 50 Hz and 120 Gauss. Two magnetic field strengths were passed through an AC magnetic field generator and random orientation treatment was performed. Further, a method in which the calendering of the non-magnetic layer is not performed may be adopted. Production method 4 (computer tape: W / D) The above-mentioned paints were kneaded with a kneader, and then dispersed using a sand mill. To the obtained dispersion, 2.5 parts of polyisocyanate is added to the coating solution for the non-magnetic layer, 3 parts to the coating solution for the magnetic layer, and 40 parts of cyclohexanone is added to each, to have an average pore diameter of 1 μm. The solution was filtered using a filter to prepare a coating solution for forming a nonmagnetic layer and a coating solution for forming a magnetic layer.

An aramid support (trade name: MICRON) having a thickness of 4.4 μm and a center plane average surface roughness of 2 nm was applied to the obtained nonmagnetic layer coating solution so that the thickness after drying became 1.7 μm. After coating and drying once and calendering, a magnetic layer is further coated thereon by a blade method so that the magnetic layer has a thickness of 0.15 μm, and a cobalt magnet having a magnetic force of 6000 G and a It was oriented by a solenoid having magnetic force. The subsequent steps were performed in the same manner as in Production Method 2. Further, a method in which the calendering of the non-magnetic layer is not performed may be adopted. Production method 5 (disk: spin coating) For each of the above 10 paints, each component was kneaded with a kneader and then dispersed using a sand mill. In the obtained dispersion, polyisocyanate was added to the coating liquid for the non-magnetic layer.
0 parts, 10 parts of the coating solution for the magnetic layer, and 40 parts of cyclohexanone were added to each, and the mixture was filtered using a filter having an average pore size of 1 μm. Were adjusted respectively.

The obtained coating solution of the nonmagnetic layer was spin-coated on a polyethylene terephthalate support having a thickness of 62 μm and a center plane average surface roughness of 3 nm so that the thickness after drying became 1.5 μm. After coating and drying once, a magnetic layer was further applied thereon by spin coating so that the thickness of the magnetic layer became 0.15 μm, and orientation treatment was performed in the circumferential direction with a 6000 G same-pole opposing Co magnet. . This was subjected to a batch-type rolling treatment capable of obtaining the same pressure as in Production Method 1 to smooth the surface. The subsequent steps were performed in the same manner as in Production Method 1. Alternatively, a method of spin-coating the non-magnetic layer and spin-coating the magnetic layer on the non-magnetic layer while the non-magnetic layer is not dried may be used. The use of the spin coating method not only increases the amount of residual magnetization in the recording direction, but also reduces the perpendicular magnetization component of barium ferrite or metal magnetic powder having a short needle ratio, thereby improving the symmetry of the reproduced waveform. . Support B-1 Polyethylene terephthalate Thickness: 62 μm, F-5 value: MD 114 MPa, TD
107 MPa Breaking strength: MD 276 MPa, TD 281 MPa Breaking elongation: MD 174 MPa, TD 139 MPa Thermal shrinkage (80 ° C., 30 minutes): MD 0.04%, TD
0.05% heat shrinkage (100 ° C, 30 minutes): MD 0.2%, TD
0.3% thermal expansion coefficient: major axis 15 × 10 ^-5 / ℃, minor axis 18 ×
10 ⁻⁵ / ° C. Center plane average surface roughness 3 nm Support B-2 Polyethylene naphthalate Thickness: 55 μ, Center plane average surface roughness 1.8 nm Thermal shrinkage (80 ° C., 30 minutes): MD 0.007% , T
D 0.007% Heat shrinkage (100 ° C., 30 minutes): MD 0.02%, T
D 0.02% Thermal expansion coefficient: major axis 10 × 10 ^-5 / ° C, minor axis 11 ×
10 ^-5 / ° C Support B-3 Polyethylene terephthalate Thickness: 62 μm, center plane average surface roughness 9 nm Support B-4 Aramid Thickness 4.4 μ center plane average surface roughness 2 nm Orientation O-1 randomization Perform orientation.

After orientation in the longitudinal direction with an O-2Co magnet, randomized orientation is performed. After orienting in the longitudinal direction with an O-3Co magnet, orienting in the longitudinal direction with a solenoid. Perform vertical orientation with O-4Co magnet. Circumferential orientation is performed with an O-5 Co magnet. Back layer paint BL-1 Fine carbon black powder 100 parts [(Cabot, BP-800, average particle size: 17 mμ)] Coarse particle carbon black powder 10 parts [(Karncarb, thermal black, average particle size) : 270 mμ)] Calcium carbonate (soft inorganic powder) 80 parts [(Shiraishi Kogyo Co., Ltd., white luster O, average particle size: 40 mμ, Mohs hardness: 3)] α-alumina (hard inorganic powder) 5 parts [(average Particle size: 200 mμ, Mohs hardness: 9)] Nitrocellulose resin 140 parts Polyurethane resin 15 parts Polyisocyanate 40 parts Polyester resin 5 parts Dispersant: Copper oleate 5 parts Copper phthalocyanine 5 parts Barium sulfate 5 parts Methyl ethyl ketone 2200 parts Butyl acetate 300 Parts toluene 600 parts

The components forming the back coat layer were kneaded with a continuous kneader, and then dispersed using a sand mill. The obtained dispersion was filtered using a filter having an average pore diameter of 1 μm to prepare a coating liquid for forming a backcoat layer. Magnetic properties, center plane average roughness, areal recording density, etc. were measured for samples obtained by appropriately combining the above methods as shown in Tables 1 to 4. (1) Magnetic properties (Hc): Measured using a vibration sample type magnetometer (manufactured by Toei Kogyo Co., Ltd.) with Hm10KOe. (2) Center plane average surface roughness (Ra): 3D-MIRAU
Surface roughness (Ra): Ra, Rrms, Peak-Valley values of an area of about 250 μm × 250 μm were measured by MIRAU method using TOPO3D manufactured by WYKO. Spherical correction and cylindrical correction are added at a measurement wavelength of about 650 nm.
This method is a non-contact surface roughness meter that measures by light interference. (3) The areal recording density is obtained by multiplying the linear recording density by the track density. (4) The linear recording density is the number of bits of a signal recorded per inch in the recording direction. (5) Track density is the number of tracks per inch. (6) φm is the amount of magnetization per unit area of the magnetic recording medium. Bm (Gauss) multiplied by the thickness, using a vibrating sample magnetometer (Toei Kogyo Co., Ltd.)
It is a value measured with Hm10kOe and can be directly measured. (7) The error rate of the tape is obtained by recording the signal of the above linear recording density on the tape by the 8-10 conversion PR1 equalization method, and
It measured using the S drive. (8) The error rate of the disk was measured by recording the signal of the above linear recording density on the disk by the (2,7) RLL modulation method. (9) Thickness of the magnetic layer A magnetic recording medium was cut out to a thickness of about 0.1 μm with a diamond cutter over a longitudinal direction, and the transmission electron microscope was used to magnify 10,000 to 10,000 times.
Observation was performed at a magnification of 0, preferably 20,000 to 50,000, and the photograph was taken. Photo print size is A
4-A5. Thereafter, the interface was visually judged by paying attention to the shape difference between the ferromagnetic powder and the nonmagnetic powder of the magnetic layer and the lower nonmagnetic layer, and the surface of the magnetic layer was similarly blackened. Thereafter, the length of the cut line was measured by an image processing apparatus IBAS2 manufactured by Zeiss. Sample photo length is 2
In the case of 1 cm, the measurement was performed 85 to 300 times. The average of the measured values at that time was d, and the standard deviation σ of the measured values was d. d is σ according to the description in JP-A-5-298655.
Was calculated by Equation 2. di is each measured value, n
Is 85 to 300.

[0098]

[Table 1]

[0099]

[Table 2] In Examples 18 to 20 and Reference Example 1, the disk of Example 13 was used, and the error rate was measured similarly while changing the linear recording density and the track density.

[0100]

[Table 3]

[0101]

[Table 4] As described above, the error rate is obtained by converting the signal of the above linear recording density to 8
-10 conversion Measured using a DDS drive after recording on a tape by the PR1 equalization method. Examples 30 and 31, Reference Example 2
The error rate was similarly measured using the tape of Example 24 while changing the linear recording density and the track density.

From the results in the above table, it can be seen that the magnetic recording medium of the present invention is much better than the conventional disk-shaped medium, especially when the error rate in the high-density recording area is 10 ^-5 or less. It can also be seen that the error rate of the computer tape is remarkably good at an error rate of 10 ^-5 or less.

[0103]

According to the present invention, a substantially nonmagnetic lower layer and a ferromagnetic metal fine powder or a ferromagnetic hexagonal ferrite fine powder are dispersed in a binder on a nonmagnetic support. In the provided magnetic recording medium, the areal recording density of the magnetic recording medium is 0.2 to ² Gbit / inch ² , the dry thickness of the magnetic layer is 0.05 to 0.25 μm, and Φ
m is 8.0 × 10 ^{−3 to} 1.0 × 10 ⁻³ emu / cm ² ,
The coercive force of the magnetic layer is 1800 Oe or more, and the lower layer and / or the magnetic layer is at least a saturated fatty acid;
By using a magnetic recording medium characterized by containing an unsaturated fatty acid and a saturated or unsaturated fatty acid ester, excellent high-density properties and excellent high-density properties that cannot be obtained by conventional coating-type magnetic recording medium technology It is possible to obtain a magnetic recording medium having a significantly improved error rate in a high-density recording area having high durability.

Claims (7)

[Claims] 1. A magnetic recording medium comprising a support and a substantially nonmagnetic lower layer and a magnetic layer formed by dispersing a ferromagnetic metal fine powder or a ferromagnetic hexagonal ferrite fine powder in a binder in this order. Wherein the magnetic recording medium is a magnetic recording medium for recording a signal having an areal recording density of 0.2 to ² Gbit / inch ² , and the magnetic layer has a dry thickness of 0.05 to 0.25 μm.
m and φm is 8.0 × 10 ^{−3 to} 1.0 × 10 ⁻³
emu / cm ² , the coercive force of the magnetic layer is 1800 Oe or more, and the lower layer and / or the magnetic layer contains at least a saturated fatty acid, an unsaturated fatty acid, and a saturated or unsaturated fatty acid ester. Magnetic recording medium. 2. The magnetic recording medium according to claim 1, wherein the surface recording density is
0.35-2 Gbit / inch ^TwoMagnetic recording medium for recording signals
Inorganic powder having a Mohs hardness of 4 or more in the lower layer
2. The magnetic recording medium according to claim 1, comprising: 3. The dry thickness of the magnetic layer is 0.05 to 0.5.
2. The magnetic recording medium according to claim 1, wherein the magnetic layer contains an abrasive having an average particle size of not more than 0.4 [mu] m. 4. The magnetic recording medium according to claim 1, wherein the coercive force of the magnetic layer is 2000 Oe or more. 5. The saturated fatty acid and unsaturated fatty acid are monobasic fatty acids having 10 to 24 carbon atoms (they may be branched).
The magnetic recording medium according to the above. 6. The saturated or unsaturated fatty acid ester is a monobasic fatty acid having 10 to 24 carbon atoms (which may be branched) and monovalent, divalent, trivalent or tetravalent having 2 to 12 carbon atoms. ,
Mono- or di-fatty acid esters or tri-fatty acid esters comprising any one of pentavalent and hexavalent alcohols (which may be branched), and fatty acid esters of monoalkyl ethers of alkylene oxide polymers. 3. The magnetic recording medium according to claim 1, wherein: 7. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a disk.